Stan J

Add this to your functions.php:

add_action('admin_head', 'remove_yoast_branding_backend');
	function remove_yoast_branding_backend()
    {
        ?>
        <style type="text/css">
            div[class*="yoast_"] {
                display: none !important;
            }
        </style>
        <?php
    }

Does the trick 🙂